How to visualize a quantum transition of a single atom

The previously proposed visualization of Rabi oscillations of a single atom by a continuous fuzzy measurement of energy is specified for the case of a single transition between levels caused by a pi-pulse of a driving field. An analysis in the framework of the restricted-path-integral approach (which reduces effectively to a Schrodinger equation with a complex Hamiltonian) shows that the measurement gives reliable information about the system evolution, but the probability of the transition becomes less than unity. In addition an experimental setup is proposed for continuously monitoring the state of an atom by observation of electrons scattered by it. It is shown how this setup realizes a continuous fuzzy measurement of the atom energy. (C) 1997 Elsevier Science B.V.